L-tryptophan-induced eosinophilia-myalgia syndrome. II. Partial correction of abnormal tryptophan metabolism by pyridoxine.

Abnormal metabolism of tryptophan is one of the possible aetiological factors in the L-tryptophan-induced eosinophilia-myalgia syndrome (EMS). We studied the plasma levels of tryptophan and serotonin and the urinary excretion of kynurenine and 5-hydroxyindoleacetic acid after oral intake of L-tryptophan in 1 subject with EMS and 2 healthy subjects. The test was repeated with concomitant administration of pyridoxine. In the patient there were elevated levels of plasma tryptophan during the loading and increased elimination of kynurenine in the urine both during and after the L-tryptophan test. During pyridoxine administration tryptophan levels and kynurenine elimination were much reduced, and kynurenine elimination was similar to that of controls. This study (i) confirms that an abnormal metabolism of L-tryptophan occurs in EMS patients and (ii) shows that this can be corrected by pyridoxine.